1. Technical Field
The present invention relates to an oscillator, an electronic apparatus, and a moving object.
2. Related Art
A crystal oscillator used in a reference frequency signal source of a communication apparatus, a measuring instrument, and the like is requested to have a stable output frequency at high accuracy with respect to a temperature change. In general, as a crystal oscillator that can obtain extremely high frequency stability among crystal oscillators, an oven controlled crystal oscillator (OCXO) is known. Further, in recent years, improvement of characteristics of a temperature compensated crystal oscillator is remarkable. A temperature compensated crystal oscillator (TCXO) having frequency accuracy and frequency stability close to those of the OCXO is being developed.
Such an oscillator having high accuracy is used in, for example, a cellular phone base station. The oscillator is sometimes requested to be capable of controlling a frequency according to digital control. JP-A-2011-101212 (Patent Literature 1) discloses a piezoelectric oscillator including a D/A converter, a vibrator, and an oscillation loop circuit. The piezoelectric oscillator changes an input signal to the D/A converter to thereby change a frequency output from the piezoelectric oscillator.
However, in the oscillator described in Patent Literature 1, an output voltage of a reference-voltage generation circuit, which supplies a voltage to the D/A converter, fluctuates because of a change in an ambient temperature (an outside temperature) of the oscillator. FIG. 77 is a graph showing an example of a temperature characteristic (a relation between an output voltage and temperature) of a regulator configuring the reference-voltage generation circuit. As shown in FIG. 77, the output voltage of the regulator greatly fluctuates because of the temperature thereof. In the oscillator explained above, if the temperature of the reference-voltage generation circuit fluctuates due to the change in the ambient temperature of the oscillator and the output voltage of the reference-voltage generation circuit greatly fluctuates, even if a DAC control code (digital data) input to the D/A converter is the same, an output voltage of the D/A converter fluctuates. As a result, the frequency output by the oscillator fluctuates.